The invention relates to a thin film photodetector, method and system, particularly to a thin film thermoelectric configured photodetector and more particularly to a photovoltaic cell with integral structure.
A thin film photodetector, for example a photovoltaic cell converts energy into electricity. Thin film photodetectors find application in photovoltaic devices Including solar cells, infrared sensors and photonic devices that absorb laser light that are applied in high speed optical transmission systems, for example as electro-absorption modulators, waveguide photodetectors, and semiconductor Mach-Zender modulators.
A thin film photovoltaic cell photogenerates charge carriers (electrons and holes) in a light-absorbing material, and separates the charge carriers to a conductive contact that transmits electricity. For example, a photovoltaic cell detects photons radiatively emitted by a light source. The cell converts the incident photons to charge carriers (electrons and holes) in a light absorbing material and the charge carriers are separated to a conductive contact that transmits electricity.
The wavelength (λ) of an incident photon is inversely proportional to its photon energy and can be calculated from λ=hc/E where h is Planck's constant and c is the speed of light. Photons with energy greater than the semiconductor bandgap (Eg) (typically ranging from 0.50 to 0.74 eV for photovoltaic devices) excite electrons from the valence band to the conduction band of the semiconductor material (interband transition). The resulting electron-hole pairs are then collected and used to power electrical loads. Photons with energy less than the semiconductor bandgap cannot be converted to electrical energy and, therefore, are parasitically absorbed as heat. In some systems, improved photovoltaic conversion efficiency is attained by reducing the amount of below bandgap energy that is parasitically absorbed. But these mechanisms only depreciate the conversion efficiency of total incident photon energy to electric power by diverting some energy (albeit in the form of heat) away from the cell.
There is a need for an improved photodetector that converts a higher proportion of available photon energy into useable electric energy and method and system.